Fiberglass is manufactured from various raw materials combined in specific proportions to yield a desired chemical composition. This proportion is commonly termed a “glass batch.” The composition of the glass batch and the glass manufactured from it are typically expressed in terms of percentages of the components, which are expressed as oxides. SiO2, Al2O3, CaO, MgO, B2O, Na2O, K2O, Fe2O3, and minor amounts of other oxides are common components of a glass batch. Numerous types of glasses may be produced from varying the amounts of these oxides, or eliminating some of the oxides, in the glass batch. Examples of such glasses that may be produced include E-glass, S-glass, R-glass, A-glass, C-glass, and ECR-glass. The glass composition determines the properties of the glass including properties such as the viscosity, the liquidus temperature, the durability, the density, the strength, and the Young's modulus of the glass. Non-physical considerations given to commercial glass compositions include the raw material cost and environmental impact caused by manufacturing the glass.
E-glass compositions are the most common glass compositions for making continuous glass fiber strands used in textile and reinforcement applications. One advantage of E-glass is that its liquidus temperature is approximately 200° F. below its forming temperature, which is commonly defined as the temperature at which the viscosity of the glass equals 1000 poise. E-glass has a wide range of forming temperatures and a low devitrification rate. Historically, commercial E-glass compositions possessed forming temperatures between 2150° F. and 2350° F. and liquidus values from approximately 100° F. to 250° F. below the forming temperature.
Producing glass fibers from E-glass compositions is well-known in the fiberglass industry. To be defined as an E-glass according to ASTM D578, the glass composition is composed primarily of the oxides of calcium, aluminum, and silicon. E-glass for use in glass fiber products for general applications as defined by ASTM D578 contains the components in the ranges set forth in Table 1. ASTM D578 teaches that E-glass for use in glass fiber yarn products for printed circuit boards and in aerospace applications has the components and percentages set forth in Table 2.
TABLE 1Chemical% by weightB2O3 0–10CaO16–25Al2O312–16SiO252–62MgO0–5TiO2  0–1.5Fe2O30.05–0.8 F2  0–1.0Na2O + K2O0–2
TABLE 2Chemical% by weightB2O3 5–10CaO16–25Al2O312–16SiO252–56MgO0–5TiO2  0–0.8Fe2O30.05–0.4 F2  0–1.0Na2O + K2O0–2
Attempts have been made to create or modify E-glass compositions to achieve certain desired properties or characteristics. Early efforts to develop E-glasses with good forming characteristics include U.S. Pat. No. 2,334,961 to Schoenlaub and U.S. Pat. No. 2,571,074 to Tiede, et al. The glass compositions taught by Schoenlaub and Tiede, et al. are set forth in Table 3.
TABLE 3U.S. Pat.U.S. Pat.No. 2,334,961No. 2,571,074(Schoenlaub)(Tiede, et al.)Chemical% by weight% by weightB2O3 9–11 8–13CaO16–1919–25Al2O312–1612–16SiO252–5652–56MgO3–6—
To form glass fibers, typically the glass batch is melted, the molten glass is drawn into filaments through a bushing or orifice plate, and an aqueous sizing composition containing lubricants, coupling agents, and film-forming binder resins is applied to the filaments. After the sizing composition is applied, the fibers may be gathered into one or more strands and wound into a package or, alternatively, the fibers may be chopped while wet and collected. The collected chopped strands may then be dried and cured to form dry chopped fibers or they can be packaged in their wet condition as wet chopped fibers.
Current glass compositions, including current E-glass compositions, have a high forming viscosity that requires the use of bushings made from platinum and rhodium. Platinum-rhodium bushings are expensive and increase the manufacturing costs of the glass fibers and products or articles formed from the glass fibers.
Despite the existence of E-glass compositions, there is an existing need in the art for improved or new E-glass compositions that meet the requirements of ASTM D578, that maintain or exceed the physical properties of conventional E-glass compositions, and that possess a viscosity that is low enough to utilize a platinum and rhodium-free bushing and reduce the manufacturing costs associated with the production of E-glass fibers.